The present invention relates to a packing method and a packing apparatus in which a powder, a granular material, a material in flakes, a plate material or the like (hereinafter collectively referred to as the xe2x80x9cmaterialxe2x80x9d) is injected into a container or receptacle such as a can, a bag, a rubber mold, a die or the like (hereinafter collectively referred to as the xe2x80x9ccontainerxe2x80x9d) which has an opening for feeding the material and a space of which is filled with said powder or the like.
Japanese patent applications commonly assigned with this application and published as KOKAI H9-78103, KOKAI H9-169301, and KOKAI H11-49101, and in commonly assigned U.S. Pat. No. 5,725,816 disclose packing a container, a can, a bag, a rubber mold, a die or the like with a material by using an air-tapping method.
By adopting said air packing method, scattering in quantity of the material at each time of the filling has been decreased, and the regional difference in packing density of the material in the container has been lessened.
Referring to FIGS. 5, 6, and 7, this earlier disclosed air packing methods are hereinafter described. Here, a die and a punch inserted into said die form a container into which a powder is injected.
A part (1) shown in FIG. 5 is a cylindrical die, and part (2) is a punch inserted into the die (1) (hereinafter this punch is referred to as the xe2x80x9clower punchxe2x80x9d). A powder is to be filled into a die cavity (3) which is a space formed with the die (1) and the lower punch (2). A table (4) is arranged so that its upper surface is flush with the upper surface (1a) of the die (1). A box-shaped, bottomless feeding element (hereinafter referred to as the xe2x80x9cfeed shoexe2x80x9d) (5) is mounted on the table (4). The external wall of the receded part of the feed shoe (5) is provided with a pipe (6), which is connected to an aspirator-type vacuum generator (7). A pipe (8) connected to the external wall (5a) of the feed shoe (5) is connected to a compressed air supplier (10) through an electromagnetic valve (9). A part (11) is a cover attached to the upper opening of the part (5a) of the feed shoe (5). The feed shoe (5) is loaded with a powder (p). A horizontal cylinder (12) is attached to the table (4), and a piston rod (12a) attached to the horizontal cylinder is connected to the feed shoe (5).
In order to fill the die cavity (3), which is formed with the die (1) and the lower punch (2) inserted into said die (1), with the powder (p), the feed shoe (5) mounted on the table (4) is moved by driving the horizontal cylinder (12) so as to move the piston rod (12a) until the feed shoe (5) is located above the die cavity (3) as shown in FIG. 6. Then, the powder (5) stored in the feed shoe (5) falls into the die cavity (3).
Subsequently, the aspirator-type vacuum generator (7) is energized with the electromagnetic valve (9) being closed so that air in the feed shoe (5) is let out, thereby changing the air-pressure inside the feed shoe (5) from the atomospheric state (a) to a state lower than the atmospheric pressure (b). FIG. 7 shows an example in which the lower state (b) is 0.5 atm. Then, by stopping deaeration by the aspirator-type vacuum generator (7) and opening the electromagnetic valve (9), the feed shoe (5) is supplied with compressed air from the compressed air supplier (10), and the air-pressure state inside the feed shoe (5) is brought into a state at least higher than the air-pressure state (b) described above. In FIG. 7, the air-pressure inside the feed shoe is brought into 0.8 atm, which is higher than the air-pressure state (b). When the air-pressure inside the feed shoe (5) has become higher than the air-pressure state (b) which is lower than the atmospheric pressure, the electromagnetic valve (9) is again closed and the aspirator-type vacuum generator (7) is energized so that the inside of the feed shoe (5) is brought into a state (b) lower than the atmospheric pressure. Subsequently, operation of the aspirator-type vacuum generator (7) is stopped and electromagnetic valve (9) is opened so that the inside of the feed shoe (5) is supplied with compressed air, thereby changing the state inside the feed shoe (5) from the air-pressure state (b) to a air-pressure state (c) higher than the air-pressure state (b).
As discussed above, by the air tapping method in which the air-pressure state inside the feed shoe is repeatedly switched from a state (b) which is lower than the atmospheric pressure to a state (c) which is higher than the state (b), the die cavity (3) formed with the die (1) and lower punch (2) inserted therein may be filled with the powder (p) homogeneously and highly densified. After the powder (p) is packed into the die cavity (3), the horizontal cylinder (12) is moved so as to retract the piston rod (12a), thereby relocating the feed shoe (5) away from the die cavity (3). Then, an upper punch (not shown in the Figure) is inserted into the die (1) and lowered to press the powder (p) packed in the die cavity (3) so as to obtain a powder compact.
The earlier methods in which filling is carried out not by air tapping but only by gravity suffer problems that: the packing quantity varies at each time of packing, the packing density varies regionally in the container, and the packing quantity of each container is uneven when filling multiple containers at the same time. In particular, when a cavity with a complex shape or with a shallow ring shape is filled with a powder by the filling methods without the use of air tapping, the unevenness of the packing density in the cavity greatly deteriorates the quality of the product.
By adopting air tapping to fill a container with a material, the problems as described above may be prevented. However, in the earlier air tapping method and apparatuses described above, air tapping is carried out by the repetition of switching the air-pressure state from a state (b), which is lower than the atmospheric pressure, to a state (c), which is higher than the state (b), a problem arises when the air-pressure inside the feed shoe (5) becomes lower than the atmospheric pressure. That is, the air outside the die cavity (3) flows into the die cavity (3) through the clearance between the internal wall (1b) of the die (1) and the external wall (2a) of the lower punch (2), which blows up the powder (p) packed in the die cavity (3).
In addition, when the earlier air tapping method is used for filling a rubber mold (17) shown in FIG. 3 with a powder, since the air-pressure state inside the rubber mold (17) becomes lower than the atmospheric pressure when it is at the low air-pressure state in the air tapping process, it is necessary to prevent the rubber mold from deforming inwardly by resorting to means for bringing the outside of the rubber mold also into a low air-pressure state. Such a preventive measure complicates the structure of the apparatus, causing the apparatus to be costly and trouble prone.
It is an object of the present invention to solve the problems that the earlier packing methods and apparatuses suffered.